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Add QgsHistogram class for calculating numeric histograms from a

list of values or a vector layer's attribute.
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nyalldawson committed May 2, 2015
1 parent 7091d3b commit 17962ef47b48dd8e4788fbfc7fe5cad7b414171e
@@ -43,6 +43,7 @@
%Include qgsgeometry.sip
%Include qgsgeometryvalidator.sip
%Include qgsgeometrysimplifier.sip
%Include qgshistogram.sip
%Include qgsmaptopixelgeometrysimplifier.sip
%Include qgsgml.sip
%Include qgsgmlschema.sip
@@ -0,0 +1,66 @@
/** \ingroup core
* \class QgsHistogram
* \brief Calculator for a numeric histogram from a list of values.
*
* \note Added in version 2.9
*/

class QgsHistogram
{
%TypeHeaderCode
#include "qgshistogram.h"
%End

public:

QgsHistogram();

virtual ~QgsHistogram();

/** Assigns numeric source values for the histogram.
* @param values list of doubles
*/
void setValues( const QList<double>& values );

/** Assigns numeric source values for the histogram from a vector layer's field or as the
* result of an expression.
* @param layer vector layer
* @param fieldOrExpression field name or expression to be evaluated
* @returns true if values were successfully set
*/
bool setValues( QgsVectorLayer* layer, const QString& fieldOrExpression );

/** Calculates the optimal bin width using the Freedman-Diaconis rule. Bins widths are
* determined by the inter-quartile range of values and the number of values.
* @returns optimal width for bins
* @see optimalNumberBins
* @note values must first be specified using @link setValues @endlink
*/
double optimalBinWidth() const;

/** Returns the optimal number of bins for the source values, calculated using the
* Freedman-Diaconis rule. The number of bins are determined by the inter-quartile range
* of values and the number of values.
* @returns optimal number of bins
* @see optimalBinWidth
* @note values must first be specified using @link setValues @endlink
*/
int optimalNumberBins() const;

/** Returns a list of edges for the histogram for a specified number of bins. This list
* will be length bins + 1, as both the first and last value are also included.
* @param bins number of bins
* @return list of bin edges
* @note values must first be specified using @link setValues @endlink
*/
QList<double> binEdges( int bins ) const;

/** Returns the calculated list of the counts for the histogram bins.
* @param bins number of histogram bins
* @return list of histogram counts
* @note values must first be specified using @link setValues @endlink
*/
QList<int> counts( int bins ) const;

};

@@ -107,6 +107,7 @@ SET(QGIS_CORE_SRCS
qgsgeometryvalidator.cpp
qgsgml.cpp
qgsgmlschema.cpp
qgshistogram.cpp
qgslayerdefinition.cpp
qgslabel.cpp
qgslabelattributes.cpp
@@ -510,6 +511,7 @@ SET(QGIS_CORE_HDRS
qgsfontutils.h
qgsgeometry.h
qgsgeometrycache.h
qgshistogram.h
qgslayerdefinition.h
qgslabel.h
qgslabelattributes.h
@@ -0,0 +1,125 @@
/***************************************************************************
qgshistogram.cpp
----------------
begin : May 2015
copyright : (C) 2015 by Nyall Dawson
email : nyall dot dawson at gmail dot com
***************************************************************************/

/***************************************************************************
* *
* This program is free software; you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
* the Free Software Foundation; either version 2 of the License, or *
* (at your option) any later version. *
* *
***************************************************************************/

#include "qgshistogram.h"

#include "qgsstatisticalsummary.h"
#include "qgsvectorlayer.h"
#include <qmath.h>

QgsHistogram::QgsHistogram()
: mMax( 0 )
, mMin( 0 )
, mIQR( 0 )
{

}

QgsHistogram::~QgsHistogram()
{

}

void QgsHistogram::prepareValues()
{
qSort( mValues.begin(), mValues.end() );

QgsStatisticalSummary s;
s.setStatistics( QgsStatisticalSummary::Max | QgsStatisticalSummary::Min | QgsStatisticalSummary::InterQuartileRange );
s.calculate( mValues );
mMin = s.min();
mMax = s.max();
mIQR = s.interQuartileRange();
}

void QgsHistogram::setValues( const QList<double> &values )
{
mValues = values;
prepareValues();
}

bool QgsHistogram::setValues( QgsVectorLayer *layer, const QString &fieldOrExpression )
{
mValues.clear();
if ( !layer )
return false;

bool ok;
mValues = layer->getDoubleValues( fieldOrExpression, ok );
if ( !ok )
return false;

prepareValues();
return true;
}

double QgsHistogram::optimalBinWidth() const
{
//Freedman-Diaconis rule
return 2.0 * mIQR * qPow( mValues.count(), -1 / 3.0 );
}

int QgsHistogram::optimalNumberBins() const
{
return ceil(( mMax - mMin ) / optimalBinWidth() );
}

QList<double> QgsHistogram::binEdges( int bins ) const
{
double binWidth = ( mMax - mMin ) / bins;

QList<double> edges;
edges << mMin;
double current = mMin;
for ( int i = 0; i < bins; ++i )
{
current += binWidth;
edges << current;
}
return edges;
}

QList<int> QgsHistogram::counts( int bins ) const
{
QList<double> edges = binEdges( bins );

QList<int> binCounts;
binCounts.reserve( bins );
int currentValueIndex = 0;
for ( int i = 0; i < bins; ++i )
{
int count = 0;
while ( mValues.at( currentValueIndex ) < edges.at( i + 1 ) )
{
count++;
currentValueIndex++;
if ( currentValueIndex >= mValues.count() )
break;
}
binCounts << count;
}

if ( currentValueIndex < mValues.count() )
{
//last value needs to be added
binCounts[ bins - 1 ] = binCounts.last() + 1;
}

return binCounts;
}


@@ -0,0 +1,97 @@
/***************************************************************************
qgshistogram.h
--------------
begin : May 2015
copyright : (C) 2015 by Nyall Dawson
email : nyall dot dawson at gmail dot com
***************************************************************************/

/***************************************************************************
* *
* This program is free software; you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
* the Free Software Foundation; either version 2 of the License, or *
* (at your option) any later version. *
* *
***************************************************************************/

#ifndef QGSHISTOGRAM_H
#define QGSHISTOGRAM_H

#include <QList>

class QgsVectorLayer;


/** \ingroup core
* \class QgsHistogram
* \brief Calculator for a numeric histogram from a list of values.
*
* \note Added in version 2.9
*/

class CORE_EXPORT QgsHistogram
{
public:

QgsHistogram();

virtual ~QgsHistogram();

/** Assigns numeric source values for the histogram.
* @param values list of doubles
*/
void setValues( const QList<double>& values );

/** Assigns numeric source values for the histogram from a vector layer's field or as the
* result of an expression.
* @param layer vector layer
* @param fieldOrExpression field name or expression to be evaluated
* @returns true if values were successfully set
*/
bool setValues( QgsVectorLayer* layer, const QString& fieldOrExpression );

/** Calculates the optimal bin width using the Freedman-Diaconis rule. Bins widths are
* determined by the inter-quartile range of values and the number of values.
* @returns optimal width for bins
* @see optimalNumberBins
* @note values must first be specified using @link setValues @endlink
*/
double optimalBinWidth() const;

/** Returns the optimal number of bins for the source values, calculated using the
* Freedman-Diaconis rule. The number of bins are determined by the inter-quartile range
* of values and the number of values.
* @returns optimal number of bins
* @see optimalBinWidth
* @note values must first be specified using @link setValues @endlink
*/
int optimalNumberBins() const;

/** Returns a list of edges for the histogram for a specified number of bins. This list
* will be length bins + 1, as both the first and last value are also included.
* @param bins number of bins
* @return list of bin edges
* @note values must first be specified using @link setValues @endlink
*/
QList<double> binEdges( int bins ) const;

/** Returns the calculated list of the counts for the histogram bins.
* @param bins number of histogram bins
* @return list of histogram counts
* @note values must first be specified using @link setValues @endlink
*/
QList<int> counts( int bins ) const;

private:

QList<double> mValues;
double mMax;
double mMin;
double mIQR;

void prepareValues();

};

#endif // QGSHISTOGRAM_H
@@ -156,4 +156,5 @@ ADD_QGIS_TEST(imageoperationtest testqgsimageoperation.cpp)
ADD_QGIS_TEST(painteffecttest testqgspainteffect.cpp)
ADD_QGIS_TEST(painteffectregistrytest testqgspainteffectregistry.cpp)
ADD_QGIS_TEST(statisticalsummarytest testqgsstatisticalsummary.cpp)
ADD_QGIS_TEST(histogramtest testqgshistogram.cpp)

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